Method for displaying an object design

ABSTRACT

The disclosure presents methods to enable and facilitate the display, visualization and realization of a two-dimensional design on a three-dimensional object. Methods for the creation of the design using a Virtual Design Environment, alone or in conjunction with an Optical Projection System, for the application of the design onto a three-dimensional real world object, are proposed, and improvements to a Laser System for displaying the design on the object.

This application claims the benefit of provisional application60/025,334 filed Sep. 3, 1996.

This invention relates to a Virtual Design System that uses amathematical 3D model of a real world object, performs an application ofa design on that model, and which can be combined with an OpticalProjection System to visualize the design and/or design data on the realworld object.

Standard 3D-CAD (Computer Aided Design) systems are at present widelyused or the realization and visualization of designs on objects. Thisincludes the representation of an object from different perspectives,change of light sources, shadowing, rendering, animation, and relatedfeatures. These standard systems represent a real world objectinternally as a mathematical model, which incorporates thethree-dimensional data of the object in form of primitives such aslines, polygons and solid bodies, and an instruction set of theoperations which can be performed to manipulate the data. Application ofdesigns on 3D objects with help of these systems is done in the form ofrendering techniques. Bitmap patterns are projected on the 3D-object forvisualization purposes only, this is called texture mapping. Forexample, a fashion design is evaluated visually by trying out differenttextures and color combinations on different parts of the design.

With the presently available methods, there are three main difficulties:

1. Usually, the design is done in a pure 2D environment. The consequenceis that inconsistencies, such as unexpected perspective views and generaunaesthetic effects, do not appear until the design has been applied toa real 3D object Such late findings can be very costly.

2. The application of a design onto a real 3D object is a tedious,messy, error-prone, unreproducable and time-consuming process. Thedecoration lines, masks and templates are positioned either in acomplicated manual process, or with large inaccuracies due to individualdifferences in aesthetic perceptions.

3. The application of designs on virtual 3D objects using CAD softwarewith texture mapping techniques provides a visualization of the designed3D object, but does not provide accurate data for the application of thedesign on the real world object. The consequences are then as in point2.

The present method is intended to give an artist or designer thepossibility of applying designs onto 3D objects imported from CADsystems in form of surface or solid models and generate data that willbe shared by production (meaning here the actual application of the 3Ddesign onto the real object by means of an Optical Projection System,such work being for example: the application of templates. bands,ribbons and other decorating aid that is applied prior to painting ordecorating an object, or simply the visualization of the design outlineon the real object), engineering (providing the possibility to giveinstant feedback to the providers of the CAD model or the technicaldesigners) and marketing or sales (for example for the presentation ofthe decorated CAD model to a customer, or for the generation of acomputer animation). The subject matters of the document U.S. Pat. No.5,490,080 are a method and a device for decorating a tridimensionalobject wherein a computer visualizes in advance the expected result.This method has the disadvantage that applications of designs onnon-flat surfaces often lead to unacceptable distortions of the designs.Such findings often occur at a late stage when the real object hasalready been decorated, leading to costly re-work or even redesigningfrom scratch.

Contrary to traditional methods, in the present patent application, thecomplete design process occurs in a 3D Virtual Design Environment usinga special 3D-CAD system. The production of a 3D decoration can then betested virtually, avoiding inconsistencies and errors. And contrary tosome previous design processes that use the 3D capabilities ofcomputers, not only the visualization data, but also the exact data ofthe design applied onto the 3D object is used for the design process.The exact 3D data of the design work is used subsequently by an opticalprojection system. In the present patent application, the opticalprojection is done with a Laser Projection System or other OpticalProjection Systems. An improved Laser Projection System is presented,previous proposals of such systems are described in US. Pat. Nos.5,341,183, or 5,388,318. The Optical Projection System allows thevisualization, now on the real world object, of the results obtained bythe virtual design application using the CAD system. Further on, in thepresent invention, additional data gained from the 3D-CAD system duringthe design process can be used in manufacturing. measurement andalignment processes. As an example, object details and materialcharacteristics can be incorporated

More specifically, the object of the present invention is to allow rapidcorrection of errors such as unwanted geometric distortions and to avoidprojection occlusions.

This object is solved by a method of generating a design according toclaim 1.

Further embodiments are disclosed in the subclaims. into the computeraided design process, imposing constraints on the design and assistingthe designer during the application of the design on the real worldobject (e.g. constraints on the design due to the position of doors,windows, pilots, antennas, etc. on the real object).

Note regarding nomenclature:

The term projection is used here for two different situations:

A) When denoting the 2D to 3D projection done by the artist whendesigning using the Virtual Design Environment of the computer.

B) When denoting the process of the physical projection e.g. of theoptical light beam (laser or other) onto the real 3D object, using theOptical Projection System.

Similarly, the term 3D object is referred to in two differentsituations:

A) When denoting the virtual, or 3D-CAD object

B) When denoting the real, physical object

One embodiment of the method consists of the following steps:

If a 3D CAD model exists:

The designer initially starts with a two dimensional image of the designwhich he wants to apply on an object. This 2D design is incorporatedinto a CAD system which possesses an internal 3D model of the mentionedobject. The 2D draft is then projected onto the 3D model by using one ofseveral methods available, in order to be able to visualize thedecorated 3D model of the 3D object. This provides a possibility toevaluate the decorated 3D model before applying the design on a realworld object. The virtual design environment allows for an overallimproved design production. The reasons for the improvements aremanifold. Applications of designs on non-flat surfaces often lead tounacceptable distortions of the design. Such findings often occur at alate stage when the real object has already been decorated, leading tocostly re-work or even redesigning from scratch. In this method, thevisualization of the 3D object with the incorporated design allows abetter evaluation of the design at an early stage, and changes can bemade as often as required at no extra cost. If the result is notsatisfactory, the 3D decoration is redone by modifying the 2D decorationwith subsequent repetition of the 2D onto 3D projection step. This loopis repeated until the result fulfills the requirements, such as, forexample, that an insignia must be clearly discernible from certainviewing angles, or simply, that the design fulfills proposed aestheticalconsiderations.

Once approved, the decorated 3D model of the Virtual Design Environmentbecomes the new centerpiece of object definition from which:

A) Engineering can receive feedback and incorporate the decorated objectback into engineering's database. If necessary, they can modify theoriginal 3D object using motivations provided by the virtual designapplication.

B) Production or manufacturing will be able to apply the exactdecorations and other design data onto the real 3D object by using anOptical Projection System in conjunction with the data generated by theVirtual Design Environment with 100% repeatability.

C) Marketing/sales will be able to generate replica-exactcomputer-animations and presentations of the decorated 3D object, againusing the data generated by the design environment.

The task of applying the decoration onto the real world object is donewith the assistance of Optical Projection Systems, such as a 3D-Laserprojector, as described below.

If a 3D-CAD model (either without design or with the designincorporated) does not exist:

The following cases are covered by using a special teaching (ordigitizing function available for the vector scanning Laser system(prior art):

A) The 2D design is realized and applied to the object in thetraditional way, (i.e. using templates, measuring aid, etc.) and afterthe 3D real object has been decorated, a two-projector Laser system isused to digitize (or teach-in) the approved design, e.g. using a knownmethod of triangulation, thus providing data for reproducible subsequentobject decorations.

B) The 3D decorated object already exists and the same design has to bereproduced on other objects, but no 3D CAD data of the object exists.Then again, a two-projector Laser system can be used as in A).

C) The 3D decorated object exists, for which a 3D CAD model exists, butno 3D decorated CAD model exists. In this case the two-projector Lasersystem is used to incorporate the design data and make it available forthe computer. Then, the incorporated design data can be manipulated andmodified in the virtual environment as described previously. Afterwards.the design can be applied again onto real objects.

The decorative 3D design done on a virtual 3D object using the VirtualDesign Environment generates the data fed to the Laser System that willproject the outlines (the line-artwork) accurately onto the real 3Dobject, in a fashion similar to Laser shows used for entertainment. Themain difference to Laser shows is that with the present method, thelaser projection is accurate on a 3D object, regardless of the relativeposition of the laser system. The Virtual Design Environment generatesexact data of the design in real 3D coordinates. Typical accuracies arein the range of a couple of millimeters over object sizes of 20 m, orhalf a centimeter over 50 m objects.

For the projection of the 3D-design data onto the real world objectprior art Laser Systems can be utilized. Additionally, a Laser Systemwith a number of improvements can be utilized. The improvements arepresented in this patent application. The features of the improved LaserSystem include:

1) Linewidth-control: a built-in device can dynamically vary thefocussing. This feature can be used when projecting (scanning) overvarying angles of incidence onto the surface or over varying distancesto the object. In the first case, the change of the Laser beam spot sizeas a function of angle of incidence can be influenced to a certaindecree, in the second case, the focussing is changed so as to guaranteea constant spot size over varying distances to the object within ascanned contour line. Contrary to prior art Laser Projection Systemsavailable for the type of tasks we propose. linewidth control as afunction of object properties is possible due to the informationavailable from the Virtual Design Environment.

2) Laser class 3A: The software computes the distance to the object, andautomatically modulates the Laser power in such a way that, incombination with the prior-art modulation as a function of scanningspeed, a modulation as a function of the distance to the object is done,considering the change in beam diameter and the change in scanning speedas a function of the distance. Again, modulation of the Laser power as afunction of the object distance properties is only possible due to theinformation available from the Virtual Design Environment.

3) Manual calibrations: for applications where a high accuracy is notrequired, or where periodic visual checking of reference points isenough, e.g., for positioning of templates, a lower cost Laser systemcan be used. Such a lower cost Laser system uses the same 3D projectionsoftware as the prior art Laser system, but there are no detectors orretroreflectors or detection circuits for the Laser calibration present;instead, the calibration points are targeted individually and manuallyusing a trackball, mouse or joystick, and checked visually for accuracy.In this way, no detection circuitry is needed any more. (Prior art Lasersystems use opto-electronic detection of points of reference which areused for calibration of the Laser systems to calculate their positioningrelative to the 3D object. These reference points are attached to knownpositions on the 3D object.)

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the creation of a 3D object using mathematical descriptionsand its tessellation into coplanar polygons as it is needed for the 2Donto 3D projection procedures;

FIGS. 2A-2C show the projection of a 2D design onto a 3D object usingthree different types of projection procedures;

FIG. 3 shows in detail a procedure to perform the 2D onto 3D projectionusing a computer and which allows to gain both the visualization data ofthe 3D object with the 2D design incorporated and the 3D data of thedesign on the 3D object, needed in posterior steps for the projection ofthe design on the real world object;

FIGS. 4-6 show alternative procedures to gain both the visualizationdata of the decorated 3D object and the 3D data of the design on the 3Dobject as in FIG. 3;

FIG. 7a shows a portion of a flow chart for the inventive method;

FIG. 7b shows the final portion of a flow chart shown in FIG. 7a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The design process starts with a two dimensional image of the designthat has to be visualized and/or applied on a real world object. Thereferred design is entered into a CAD-system directly exploiting thecapabilities of standard 2D-CAD software packages. Alternatively, if analready drawn design has to be processed, it can be entered into the CADsystem by using a digitizing tablet, a scanner, or similar means toincorporate design data. The internal representation of the design datauses mathematical 2D-primitives including lines, polylines, polygons,etc., with attributes such as color, texture and material properties.The 2D-data of the design is then passed to a Virtual Design 3D-CADsystem with special features for the design process.

The 3D-CAD system possesses an internal 3D model of the real worldobject onto which the design will be applied. The data for the 3D-CADmodel is normally available from the engineering/architecture-designdivisions of the company that produces,builds the real world object oris commercially available. In case that the 3D-CAD model is not directlyavailable, there is the possibility to incorporate this data with thehelp of 3D laser scanning systems or by other means. The internalrepresentation of the 3D-CAD model is described by 3D primitives such asplanes. surface elements, rotational, translational and extrusion3D-objects, and 3D solid bodies. In the following, we describe methodsto realize the application of the 2D design data onto the 3D-CAD modelin the virtual design environment.

With specific reference to FIG. 1, in the first portion 102, a commandto create a three-dimensional rotation object (cylinder) by indicationof the outline, the rotation axis and the rotational angle isillustrated. In the second portion 104, an internal representation ofthe cylinder with closed top and bottom surfaces is shown. In the thirdportion 106, decomposition of the cylinder surface into basic coplanarpolygons (tessellation) is illustrated.

The 2D-CAD design is then projected onto the 3D-CAD model of the realworld object. Difference projection methods can be used, according tothe design purpose, e.g., a central, a parallel or a cylindricalprojection, see FIGS. 2A, 2B, and 2C. For example, if the design has tobe clearly visible and detectable from a certain fixed viewpoint, acentral projection method will be used. In this case, the viewpoint foroptimal visualization falls together with the vertex of the projectionpyramid, the project center. A parallel projection method will be usedfor an approximately cylindrical or barrel-like object onto which asurrounding design has to be applied. Additionally, real world opticalprojections can be simulated with the Virtual Design Environment. Withspecific reference to FIG. 2A, an illustration of a central projectionis shown in which a projection of a two dimensional (2D) design 202 isprojected onto an idealized flat surface 204 of a three dimensional (3D)object. The projection vectors originate at a projection center 206.With specific reference to FIG. 2B, an illustration of a parallelprojection is shown in which a projection of a two dimensional (2D)design 208 is projected onto an idealized flat surface 210 of a 3Dobject. The projection vectors are orthogonal to the surface with the 2Ddesign. With specific reference to FIG. 2C, an illustration of acylindrical projection is shown in which a 2D design 212 is projectedonto a surface 214 of a 3D object. The projection vectors are orthogonalto an outer cylindrical surface with the 2D design 212.

The first virtual projection method uses both an image representationand a 2D-CAD representation of the 2D-design. While the imagerepresentation contains only texture information coded as pixel colorvalues, the 2D-CAD representation contains the vectorial informationabout the contour lines of the 2D-design. To get the data of the 2D-CADdesign projected onto the 3D-CAD model, the former is discretized (splitinto short straight line segments) and the latter is tesselated (splitinto basic, small coplanar polygons). The intersection of the projectionof each 2D-design contour segment with each 3D-polygon is thencalculated. This results in a subdivision of each 2D-design contoursegment. The parts of the contour segment that intersect with the3D-polygon compose the vector data of the 2D onto 3D design projection(see FIG. 3 for further explanations). It is used later for the LaserProjection System and for the application of the design onto the realworld object. A similar procedure has to be applied for a realisticvisualization of the design projected onto the 3D-model. Abackprojection of each 3D-polygon onto the image design plane determinesthe area of the image that corresponds to that polygon. This calculatedpart of the image is then mapped onto the 3D-polygon as a texture.Repeating the backprojection step for all 3D-polygons creates a 3D-modelwith the 2D-design image projected onto it. This can be used forvisualization purposes. It is important to notice that the sameprojection parameters have to be used both for the calculation of the2D-design projection data and for the texturing procedure of the3D-polygons with the 2D-design image. Moreover, the 2D-CADrepresentation of the 2D-design has to coincide exactly with the2D-design image representation.

With specific reference to FIG. 3, illustration 302 shows thebackprojection of a 3D model element onto the 2D design image.Illustration 304 shows 2D design image information, symbolized bydifferently shaded regions. Illustration 306 illustrates a 3D element(triangle) with texture added from the 2D design image. The texturized3D elements are used for the realistic visualization of the 3D-modelwith the 2D design image projected into it. Illustration 308 shows the3D design element with 3D contour data projected onto the 3D designelement (i.e., the 3D design segment, thick line). The data of the 3Ddesign segment is used for the Laser Projection System. Illustration 310shows the 2D design data in vector form (thick black line).Illustrations 304 and 310 show the exact correspondence of the 2D designvector data with the 2D design image data. Illustration 312 shows theprojection of the 2D design data onto the 3D model element.

In the second method, the 2D-CAD design data consists of filledpolygons. The form of the polygons is defined by the 2D-coordinates oftheir vertices. Additionally to the polygon borderlines, the 2D-designprimitives have design data incorporated, which are used in the computeraided visualization of the 2D-design projected onto the 3D-object. Thisdata consists of the colors, textures and other properties of theborderlines and internal regions of the filled polygons. To visualizethe 2D-CAD design projected onto the 3D-CAD model, both have to betesselated (split into basic, coplanar polygons). For the calculation ofthe 3D-coordinates of the design outline on the 3D-CAD model, thepolygon borders that correspond to the original design outline aremarked. Then, the intersection of the projection of each 2D-CAD elementwith each 3D-CAD element is calculated. This is illustrated in FIG. 4for the case of a central projection, in which we have a projection conethat separates the 3D-CAD element into two regions; one lying inside ofthe projection cone and one lying outside. The original 3D-CAD elementis split into new elements, and each new element lying inside of theprojection cone corresponds to the projection of the 2D-CAD element ontothe 3D-CAD model. The color, texture and material information from the2D-CAD element is assigned to this new 3D-CAD element for latervisualization purposes. Additionally, the previously marked polygonborders delimiting the 2D-design outline are used to transfer thisinformation to the new 3D-CAD elements. This information is used laterin the design application process. These steps are repeated for allelements of the 3D-CAD model and the 2D-CAD design. As a result, thiscreates a 3D-CAD model with the design data incorporated.

As a third method, standard commercially available CAD software packagescan be used (E.g. AutoCad V.12.0 or higher+AutoSurf, from AutoDesk, orMicrostation V. 6.0 or higher, from Bentley Systems). In this case, the2D-design data has to be composed of closed contour lines or curves in3D space. The contour lines or curves are normally gained defining anumber of control points and a mathematical curve definition. The closedcontours can be projected onto a 3D-surface, cutting a hole with aborderline corresponding to the projection of the 2D-design polygoncontour. Similarly, the intersection of the projection cone with the3D-surface can be computed, resulting in a 3D-surface part correspondingto the hole that was cut in the step before. Combining spatially the twoparts, one with the projection of the design outline cut into itssurface and its complement, results in 2 elements that again representthe original 3D-surface. But now, each of the two elements can beassigned its own design attributes (color, texture, material properties,etc.), enabling the CAD-system to visualize the 3D-object with thedesign incorporated. Because of the two different CAD elements, thecoordinates of the design projection can also be regained in this way,enabling the use of the design projection data with a posterior Laserprojection system or for other purposes. The method is explained in FIG.5.

With specific reference to FIG. 5, illustration 502 shows the parallelprojection of a 2D design outline 504 onto a 3D object surface 506.Illustration 508 shows a complementary element 508A gained bycomputation of the intersection of the projection trapezoid with the 3Dobject surface 506. Illustration 510 shows a hole 512 cut by theprojection of the 2D-design outline 504. Illustration 514 shows thespatial recombination of the two parts (illustrations 508, 510)incorporation the projected 2D outline and the 2D design data.

The last method consists in using solid modeling techniques available instandard 3D-CAD packages. In this case, the 3D-model has to be composedusing primitive solid bodies such as spheres, cubes or alternativelybodies defined by the rotation or the translation of a basis line (thereare other alternatives, the examples are not meant to be complete). The3D model can be composed by applying boolean operations (e.g. union ordifference) on several primitive solid bodies. The closed lines of the2D-design data are also converted into solid bodies by projection orextrusion of the original contour. This is shown in FIG. 6 for a closeddesign polyline with five points. In this particular example a solidbody for the design polyline is gained by placing the polyline in3D-space and by projecting parallel lines from all polyline vertices.This results in a solid body constructed by extrusion that can be usedfor further operations. An intersection or difference operation betweenthe 3D-model and the solid body that is gained from the 2D-designresults in a 3D-body from which the 3D-data of the 2D-design onto3D-model projection can be extracted. This is sketched in FIG. 6. Theshaded face is the surface that corresponds to the projection of the2D-curve onto the 3D-model surface. The borderline of the shaded face isthe data that is used for the posterior application of the design on thereal world object.

With specific reference to FIG. 6, a 3D model 602 is composed of solidvolumetric 3D object (shown in the example as a cube). A solid object604 is generated by a translation of a 2D design contour 606 along apathway in 3D. In illustration 608, both solids are properly locatedaccording to the 2D onto 3D projection specifications. In illustration610, an intersection operation of applied to the two solids. The shadeface 610A corresponds to the intersection of the surfaces. The thickline corresponds to the 2D design contour projected onto the 3D-model.That data of the thick line is extracted for the Laser ProjectionSystem.

The next step that follows the calculation of the projection data of the2D-design onto the 3D-object is the visualization of the 3D-CAD modelwith the 2D-design projected onto it. Here, traditional visualizationtechniques apply. As each of the new calculated elements from the 3D-CADmodel has the correct design properties assigned to it (e.g. color,texture, etc., of its borderline and its interior), this data can beused by a standard visualization algorithm. This creates a fullperspective 3-dimensional view of the 3D-CAD model decorated with the2D-CAD design. It can be evaluated from different viewpoints and underdifferent light conditions. Additionally, the new 3D-model can be usedfor further visualizations, such as animations and presentations.

From the 3D-visualization, it is easy to evaluate if the design fulfillsall necessary requirements. If this is not the case, the projection stepof the 2D-CAD design onto the 3D-CAD model is repeated. The evaluationcomprises for example examinations of design visibility from differentviewpoints, and aesthetical considerations such as the distortion of thedesign caused by the projection on an irregular surface. Anotherimportant fact is that technical details of the 3D-objects can be takeninto account at this step. For example, it can be the case that thedesign borderlines should avoid some areas of the objects surface, andthis can be easily verified at this step.

For the application of the design onto a real world object, the 3D-datafrom the projected design elements is extracted. This is done either byusing the 3D-coordinates of the projected design element segments incase of the first projection calculation method or by evaluating the3D-coordinates of the borderlines of the 3D-elements that correspond tothe borderlines of the 2D-design. These specific borderlines were markedbefore during the 2D to 3D projection step for the second, third andfourth projection calculation methods or they were explicitly calculatedfor the first calculation method, see the explanations of the virtualprojection methods of the previous pages. The data gained from this stepcontains 3D-lines and 3D polylines (consecutive connected lines definedby a list of points.). At this point, the data can be optimized for thedesign application. This will include for example an improved orderingof the sequence of output 3D-lines which takes into account thetechnical characteristics of the projection system (e.g. for themaximization of the projection speed). Another example is theoptimization of the setup locations of the one or more projectionsystems relative to the real object considering angles of incidence andocclusion (shadow) effects. The gained data is then exported to and readby a projection system coupled with the computer.

In this invention, a Laser Projection System is used for this purpose.The system reads the data from the 2D to 3D projection step and usesthis data to project the outlines of the design on the real, physicalobject. For this purpose, the data coordinates are transformed into theprojection angles for the Laser Projection System (vector-scanning LaserSystem). To be able to do this, reference points are introduced for thecalibration of the Laser System. The reference points are located at thesame position (in object-centered coordinates) on the surface of the3D-CAD model and the real world object. The 3D-coordinates of thereference points in the 3D-CAD model are passed to the projection systemtogether with the design outline data. According to standard techniques(prior art) this enables the Laser Projection System to determine itsposition relative to the real world object and thus an accurateprojection of the design outline on mentioned object.

Alternatively, other optical projection methods can be used. Theseinclude raster-scanning Laser Systems, as are used for Laser-TVtechnologies, or simple optical projectors of any kind that display thedata gained from the 2D to 3D projection step on the real object. In thecase of raster-type light projection systems, the Virtual DesignComputer System can be used to generate mathematical envelope functionsthat will distort the raster-scanned projection image in a way that whenthe projected image hits the object surface, it will do so in apredicted way and as a result give a proper intended image, free ofunwanted distortions, such as was verified during the virtual projectionstep.

The interaction of the Virtual Design Computer System with the LaserProjection System provides many benefits. First, the outcome of thedesign process can be rapidly visualized, evaluated and modified, andthus allows for rapid correction of errors such as unwanted geometricdistortions. Second, the CAD-system can calculate the optimal placingfor the Laser Projection system, e.g. avoiding projection occlusions orunder the condition that the angle of incidence of the Laser beam ontothe object surface should always be as close as possible to 90°. Third,a system with several simultaneously working Laser projectors can bebuilt, and the projection data for each system will be calculated by theCAD-system. This enables a substantial improvement of the designprocess, because the design can be applied on different parts of theobjects simultaneously. In this invention, the design step and thephysical projection/design application step are coupled, so that one canbenefit from the data obtained by the other. There is thus a directfeedback from design to realization, avoiding erroneous and thereforeexpensive steps. FIGS. 7a and 7 b present a flow diagram of the worksteps of the Virtual Design Environment coupled with a Laser ProjectionSystem as proposed in this invention.

Additionally, data other than simple visualization contours can beprojected onto the real-world object. This data can originate from the2D-design of the 3D-model information acquired by the computer system.It can provide information that accelerates or directs the designapplication process. In a projector system without a virtual designenvironment, the data of the 3D-model is not accessible and thus cannotbe incorporated in the same way.

The projection of the design data gained in the Virtual DesignEnvironment is done using optical projection systems. In this section wedescribe improvements on prior art Laser Projection Systems which can beused to project the design data created according to the precedingsection onto a real world object. The use of a Virtual DesignEnvironment allows the system to incorporate and use information intothe optical projectomata creation process that was not available before,such as the properties of the 3D-object.

1) Linewidth-control

The Laser can be equipped with a built-in device that can dynamicallyvary the focussing. This feature can be used when projecting (scanning)over varying angles of incidence onto the surface or over varyingdistances to the object. In the First case. the change of spot size as afunction of angle of incidence can be influenced to a certain degree; inthe second case. the focussing is changed so as to guarantee a constantspot size over varying distances to the object within a scanned contourline.

The device used to achieve this consists of a lens that is moved backand forth along the optical axis using either a stepper motor, agalvanometer. actuator, or any other mechanism to change the focussingof a Laser beam in a digitally controlled way. The software computes thedistance to the object, calculates the necessary aperture size toachieve the pre-defined spot size based on the Rayleigh range formula offocussing for Gaussian beams, assuming a Gaussian beam, and, based onthe optical path parameters, adjusts the dynamic focus so as to achievethe required spot size. The basic formula governing the dependence ofthe Laser linewidth on the distance is: w_(o)=f λ/πw_(s) where w_(o) isthe beam waist spot radius for a gaussian beam focussed by a lens or amirror with focal length f, for f>>W_(s), and where ws is the spot sizeat the lens or mirror and λ the Laser wavelength (Source: LaserSpectroscopy, W. Demtröder, Springer-Verlag). If, in addition, the angleof incidence of the Laser beam onto the surface is known, the softwarecomputes the same necessary dynamic focus position in order to achievethe required spot size, or the best possible spot size achievableassuming an elliptical deformation of the spot on the surface. (e.g. ifthe angle of incidence is θ, then the linewidth s on the surface at thatpoint is s=s_(o)/cos(θ), where s_(o)=2 w_(o) and w_(o) is given above.)The incorporation of the Laser linewidth control is made possible byusing the data of the virtual design environment and thus can not berealized in prior art Laser projection processes. For example, theprojector location data and the 3D-model data incorporated into thevirtual design environment is necessary to calculate angles of incidenceand similar data relevant for the described linewidth modulation. Priorart systems used this dynamic focussing to achieve a constant-size spoton flat surfaces, but not on 3D contoured surfaces.

2) Laser Class 3A

For eye-safe 3D laser scanning, the software computes the distance tothe object, and automatically modulates the Laser power in such a waythat, in combination with the prior-art modulation as a function ofscanning speed, a modulation as a function of the distance to the objectis done, considering the change in beam diameter and the change inscanning speed as a function of the distance. Using the formulas validfor rapidly scanned beams given in the CDRH Laser safety booklet, andthe fact that the dwell time of the Laser on the eye is inverselyproportional to the scanning speed, which in turn is directlyproportional to the angular scan speed and to the distance to theobject, as well as a function of the beam diameter at that distance andwhether the beam diameter is smaller or larger than the eye pupil (6mm), and using the linewidth calculation as a function of distance tothe object from above, the Laser power can be modulated in real time sothat the Laser intensity stays always below the upper limit of Class 3A.(Source: American National Standard for Safe Use of Lasers, ANSIZ136.1-1993, pg. 85, B4.6: Scanning Lasers, and European StandardEN60825, pg.29, section 13.3, and page 45, main section C. Again, thisimprovement of the Laser projection system is made possible by the dataof the virtual design environment, because it relies on the 3D-modelobject properties.

3) Manual Calibrations

The prior art vector-scanning laser projection systems need calibrationpoints on the real 3D object to ensure an accurate projection.Additionally, as the hardware is subject to drift of its electroniccomponents, they need to be periodically calibrated. Prior art systemsuse sensors or retro-reflective targets placed as reference points, anduse detection circuitry to get position feedback when the Laser isscanning the reference points. The proposed low cost improvement avoidsthe detection circuitry for the reference points. For applications wherea high accuracy is not required, or where periodic visual checking ofreference points is enough, i.e., for positioning of templates, a lowcost Laser system can be used. It uses the same 3D projection softwareto project points and lines as prior art Laser systems, but there are nodetectors or retroreflectors or detection circuits present; instead, thecalibration points, which can be simple visible elements such as boltsor rivets, are targeted individually and manually by a trackball, mouseor joystick, and checked visually for accuracy. In this way, nodetection circuitry is needed any more, although calibration proceeds asin the prior art, using the angle coordinates of the reference pointsdetermined by the operator. A coarse and a fine tune control can beincluded to allow more user comfort.

What is claimed is:
 1. A method of generating a design comprising:providing a computer system with three dimensional capabilities;providing a three-dimensional model of a real world object to thecomputer system; providing a two-dimensional design which is to beplaced on the three dimensional object; associating the two-dimensionaldesign with the three-dimensional model in the computer; providing thepossibiliy for the operator to evaluate the two-dimensional designassociated with the three-dimensional model; creating three-dimensionaldata of the two-dimensional design associated with the three-dimensionalmodel; calculating the optimal placing for an optical projection systemwith three-dimensional capabilities with respect to the real object bymeans of the computer system; and applying the three-dimensional data ofthe two-dimensional design associated with the three-dimensional modelby means of the optical projection system on the real world object.
 2. Amethod as recited in claim 1, further comprising the step of providingthe possibility for the operator to evaluate and modify the image of thetwo-dimensional design as projected by the optical projection system. 3.A method as recited in claim 1, wherein the three-dimensional model ofthe real world object in the computer is provided by digitizing thedesign on the surface of the actual three-dimensional object byutilizing a laser.
 4. A method as recited in claim 1, wherein theoptical projection system has several simultaneously working projectors.5. A method as recited in claim 1, wherein the optical projection systemis a Laser Projection system.
 6. A method as recited in claim 5, whereinthe step of applying the three-dimensional data comprises the steps of:monitoring the relative position of a laser source of the LaserProjection system and an object surface; and moving a lens along anoptical axis to control the width of the laser beam directed onto theobject in response to the monitored relative position, and to achieve adesired beam width.
 7. A method as recited in claim 6, wherein themonitored relative position is the distance between the laser source andthe object surface.
 8. The method as recited in claim 6, wherein themonitored relative position is the angle of incidence between the lasersource and the object surface.
 9. A method as recited in claim 6,wherein the step of applying the three-dimensional data comprises priorto the step of monitoring the relative position the steps of: guidingvisually the laser beam to specified calibration points on the object;and incorporating the calibration data once the laser beam is closeenough to the calibration points for manually calibrating the lasersystem with three-dimensional capabilities.
 10. A method as recited inclaim 6, wherein the step of applying the three-dimensional data furthercomprises the step of controlling the laser output as a function of themonitored relative position so that the Laser intensity stays alwaysbelow the upper limit specified in the laser safety classification.